1. Field of the Invention
This invention relates to an image display apparatus for virtual enlargement and viewing of images displayed by an image display means, and relates particularly to a head-mounted image display apparatus for viewing images with the display apparatus itself worn on the head.
2. Description of the Related Art
An apparatus which is worn on the head for viewing images is described, for example, in Japanese patent laid-open number 1993-100192. This apparatus comprises an eyeglasses-type frame which is worn on the head similarly to eyeglasses. As frequently experienced by eyeglasses users, fatigue and discomfort can occur in the nose and ears where the apparatus touches due to a slight increase in weight, and the functionality that can be provided in the image display apparatus and the viewing time are therefore limited. In addition, the apparatus may shift when the head or body is moved because the method of mounting on the head is unstable, and it is therefore not possible to view the images in a stable condition. Moreover, when the head or body is moved greatly, the apparatus may fall from the head and break.
With the head-mounted image display apparatus described in Japanese patent laid-open number 1992-22358, a pair of side frames extending to the sides of the head is provided on the apparatus, and the apparatus is mounted to the head by connecting the ends of these side frames with an elastic band and wrapping the side frames around the head. However, while this method prevents the apparatus from falling off the head by means of the elastic band, its effectiveness preventing the apparatus from falling off is insufficient because of the narrow width of the elastic band. Furthermore, even if the width of the elastic band is increased, there is still no change in the instability of the apparatus insofar as it is held only by an elastic band, and problems such as image blurring, fatigue, and discomfort remain.
Thus, the first problem with this conventional head-mounted image display apparatus is the poor user comfort resulting from the part to which the apparatus is mounted being the head, which varies in size and shape from person to person, and the difficulty of mounting the apparatus in a stable manner on the head.
Next, because the head-mounted image display apparatus is for personal use, it is possible to adjust the image display conditions according to the visual acuity and pupil distance (of the user) with the head-mounted image display apparatus described in Nikkei Electronics, No. 571, p. 119. However, this head-mounted image display apparatus is constructed to illuminate a pair of left and right optical units, each comprising a liquid crystal light valve, reflecting mirror, and enlarging lens, using one backlight, and the user experience is therefore poor. More specifically, if only the liquid crystal light valve, which is formed separately to the backlight, is moved along the optical axis of the optical unit to change the distance between the backlight and the liquid crystal light valve when the imaging position is adjusted according to the visual acuity of the user, illumination of the liquid crystal light valve also changes because divergent light is irradiated from the fluorescent tube used as the backlight, and image quality deteriorates. In particular, the right and left virtual images (luminance) will differ if the visual acuity of the user differs between the right and left eyes, and this will be a cause of asthenopia. Moreover, as the distance between the backlight and the liquid crystal light valve increases, the lighting efficiency of the backlight decreases, increasing the brightness of the image is inhibited, and attempts to overcome this become a hindrance to achieving low power consumption.
Furthermore, there are individual differences in the pupil distance, which is generally considered to be in the range of approximately 58 mm to approximately 72 mm. As a result, it is necessary for the right and left optical units to have a range of relative movement of approximately 14 mm. However, if this type of adjustment is performed separately for the right and left optical units in the conventional head-mounted image display apparatus, each eye must be separately adjusted, and more time is required. It is also possible that while this relative distance is acceptable, one of the optical units has moved too far, and use in this condition can lead to asthenopia.
With the head-mounted image display apparatus described in Japanese patent laid-open number 1993-48991, the optical axis formed by the image display apparatus, the enlargement optics, and the eye will be on the horizontal visual axis of the eye. As a result, because the viewer must view the images with the visual axis fixed in the horizontal direction, the eyelids feel forced open, the eyes and eyelids feel burdened, and this condition can lead to asthenopia if it continues for long.
The second problem is therefore the poor user comfort resulting from these conventional apparatuses not giving sufficient consideration to the characteristics of visual appreciation of information
Another head-mounted image display apparatus is described in U.S. Pat. No. 5,162,828, and others; this apparatus provides an image display element, enlargement optics for the image displayed thereby, and a holding means for positioning the enlargement optics and display element in front of the eyes of the viewer. Of these component parts, the display element has the greatest structural influence on the other parts, and is an important component; because compactness, light weight, and low power consumption are generally required in this display element, liquid crystal display elements of minimum three inches diagonally or liquid crystal display elements of a maximum one inch diagonally are used. However, major problems may result if the liquid crystal display element is either too large or too small.
First, when the liquid crystal display element is too large, the display element itself not only becomes large, the enlargement optics for enlarging and displaying the image also increase in size. As a result, the head-mounted image display apparatus becomes extremely bulky and heavy, greatly burdening the viewer. Problems relating to addressing the liquid crystal display element also occur. Specifically, because the liquid crystal display element modules are too large in the right and left optical units, they hit each other if placed in front of the eyes, and the center of the image display plane cannot be placed on the optical axis connecting the eye and the enlargement lens. In this case, the position occupied by the enlarged image is different in the viewer""s right and left visual fields, and when the brain attempts to join the right and left images when viewing television or video, the images will not completely coincide. In addition, to be recognized as a single image, it is necessary to display different images in the right and left liquid crystal display modules, making it necessary to add the circuitry and other components needed to divide and display the source image in the right and left liquid crystal display modules. The resulting problem is that it is not possible to achieve a compact, lightweight, and low cost head-mounted image display apparatus.
On the other hand, it is not possible to improve the image quality when the liquid crystal display element is too small. To improve image quality in the liquid crystal display module, it is necessary to increase the number of picture elements in the liquid crystal display element. With respect to this, however, the picture elements must be made smaller if the same number of picture elements used in the large size liquid crystal display element is to be used because the display area is small in a compact liquid crystal display element. More specifically, if the size of the liquid crystal display element is xc2xd, the picture element size also becomes xc2xd. Therefore, if a clear enlarged display image is to be obtained even though the picture element size is reduced by xc2xd, the resolution of the enlargement optics must be doubled. If the head-mounted image display apparatus is to be made smaller and lighter, however, only simple enlargement optics can be provided, and it is not possible to obtain a high quality image if the liquid crystal display element is extremely small. Furthermore, the space requirement of the thin-film transistor for switching the picture elements does not change even if the size of the picture elements is reduced. As a result, as the liquid crystal display elements become smaller, the effective aperture of the picture elements decreases, and the brightness of the display image drops. In addition, because the relative size of each picture element to the source line and the gate line decreases, the shaded part of the overall display image becomes conspicuous, and the image quality of the displayed image deteriorates.
Moreover, it is necessary to increase the magnification of the enlargement optics to obtain a wide angle of view when using compact liquid crystal display elements, and this requires using a lens with a short focal length. However, it is necessary to use a single lens for the enlargement optics in a head-mounted image display apparatus because of the need to reduce size and weight, and shortening the focal length results in using a plastic lens whereby the lens thickness can be made thick. However, because of their low precision and low throughput during mass production, thick plastic lenses ultimately reduce image quality and increase cost. Furthermore, because a very slight movement of the liquid crystal display element causes a large change in the position of virtual image formation when a short focal length lens is used and the liquid crystal display element is moved forward or back along the optical axis to adjust to the visual acuity of the user, this adjustment is difficult to accomplish without providing a precision adjustment mechanism.
The third problem is therefore poor image quality, operability, and economy resulting from the conventional apparatus being simply designed using a small display apparatus without consideration for the relationship to pupil distance, and otherwise not giving sufficient consideration to improving image quality.
With consideration to the aforementioned problems, the problem for the present invention is to provide a head-mounted image display apparatus whereby the user experience can be improved by using a construction that is sufficient adaptable to, for example, head size, pupil distance, visual acuity, and sensitivity from a human anatomical perspective.
To resolve the aforementioned problem according to the present invention, a head-mounted image display apparatus for viewing an image formed by an image display means and virtually enlarged by an enlarging means while mounted on the head is characterized by: a main apparatus comprising an image display means and an enlarging means, and comprising a frontal region support member, which is positioned at the frontal region when worn on the head, and an occipital region support member, which is positioned at the occipital region; and a securing means for holding the frontal region support member and the frontal region in contact when the main apparatus is worn on the head.
By means of this configuration, the image can be viewed from the best condition because the relationship between the position of the frontal region support member and the frontal region can be directly and reliably determined. In addition, the head-mounted image display apparatus is sufficiently adaptable to the characteristic that the place to which the main apparatus is mounted is the head, and a feeling of stability during use can be obtained.
In the present invention it is possible to use as the securing means a means comprising an inflating/deflating member that can be switched between an inflated condition and a deflated condition at that part of the inside surface of the occipital region support member contacting the occipital region.
It is also possible to use as the securing means a means comprising a displacement mechanism for moving the position of the occipital region support member on the main apparatus toward the frontal region support member, thereby relatively pushing the frontal region against the frontal region support member.
In these cases a flexible member, and preferably a buffer pad which is freely removable by means of a velcro-like material, is provided on the frontal region support member where it contacts the frontal region.
According to the present invention, a head-mounted image display apparatus for viewing an image formed by an image display means and virtually enlarged by an enlarging means while mounted on the head is characterized by: a main apparatus comprising an image display means and an enlarging means, and comprising a frontal region support member, which is positioned at the frontal region when worn on the head, and an occipital region support member, which is positioned at the occipital region; and an inflating/deflating member, which can be switched between an inflated condition and a deflated condition, on the inside of the main apparatus at least at the inside surface of the frontal region support member and the occipital region support member. In this case, inflation of the inflating/deflating member is preferably greater at the occipital region support member side than at the frontal region support member side. This is because the stability of the main apparatus in the front-back direction is improved by pressing from the back.
The inflating/deflating member of the present invention is preferably made from an air bag. This is because the apparatus is thus simplified and can be made lighter.
It is further preferable in the present invention to provide the main apparatus with: a front cover comprising an image display means, enlarging means, and frontal region support member; an occipital region support cover comprising the occipital region support member; and connecting members connecting these covers at the sides of the head; and to provide in this connecting member a support mechanism connecting the occipital region support cover to the front cover in such a manner that the occipital region support cover rotates on the support mechanism to the front cover. In this case it is preferable to provide the connecting member with a slide mechanism whereby the occipital region support cover can slide toward the front cover while the occipital region support cover remains rotatable to the front cover.
Furthermore, when speakers are built in to the connecting member, it is preferable to use the speakers as component elements of the support mechanism. Specifically, it is preferable to use the speaker frame itself as the rotational axis connecting the occipital region support cover in a rotatable manner to the front cover. In addition, an air hole passing through from the inside to the outside is preferably provided in the connecting member so that external sounds can be heard even when speakers are built in to the connecting member.
It is furthermore preferable to provide a ventilation hole in the front cover.
The present invention further preferably comprises the image display means as an integrated image display unit comprising a transparent image display member and a lighting means for illuminating this image display member from the back; comprises a pair of optical units, each integrating this image display unit with an enlarging means, housed on right and left sides in the main apparatus; and comprises a pupil distance direction position adjustment mechanism for moving the pair of optical units as a single unit in the pupil distance direction to adjust the distance between the optical axes of the optical units.
In this case, the pupil distance direction position adjustment mechanism preferably moves the optical units in the pupil distance direction by guiding a guide pin projecting from each optical unit in a guide channel formed to fit the guide pin on the side of the main apparatus. The operating knob of the pupil distance direction position adjustment mechanism is also preferably positioned at a front position of the main apparatus.
It is further preferable to provide as a diopter adjustment mechanism for each of the pair of optical units an axial position adjustment mechanism to move the image display units along the optical axis of the optical unit separately in each optical unit. It is also preferable in this case to position the operating knob of the axial position adjustment mechanism at a front position of the main apparatus.
In the present invention it is preferable to provide in the main apparatus at a position corresponding to the top of the optical unit a ventilation hole for releasing heat produced by the lighting means.
The optical axes of the optical units are also preferably set so that lines extended on the optical axes to the front intersect at the angle of convergence. This is because this angle is a more natural line of vision, and there is therefore a lesser sense of fatigue.
In addition, a reflecting mirror is preferably provided at a midpoint position of the optical axis to bend the optical axis of the optical unit. This is because the side of the image display unit and the enlarging means can be placed more three-dimensionally.
A liquid crystal light valve, for example, is preferably used as the transparent display member of the present invention.
In addition, the optical axis of the optical system including the image display means and the enlarging means preferably forms an angle of depression relative to the eye""s horizontal line of vision. This is because images can be viewed at a more natural line of vision, and there is therefore a lesser sense of fatigue. This angle of depression is 10xc2x0 or less and preferably 6xc2x0 or less.
The image display means of the present invention can be made as a pair of right and left liquid crystal display modules of liquid crystal display elements mounted on a circuit board; the liquid crystal display module is preferably designed to satisfy the equation
W1 less than G
where W1 is the horizontal width of the liquid crystal display module in millimeters, and G is the center-center distance between the right and left liquid crystal display elements in millimeters.
It is sufficient here to set the center-center distance between the right and left liquid crystal display elements to approximately 55 mm.
When the enlarging means comprises a single magnifying lens in the present invention, the liquid crystal display module is designed to satisfy the following equation
30xc3x9710xe2x88x923=P=0.0021xc3x97W2
where W2 is the horizontal width of the image display surface of the liquid crystal display element in millimeters, and P is the pixel pitch in millimeters.
In this case, the horizontal angle of view of the enlarged virtual image is preferably 30xc2x0 or greater to improve the image quality.
The liquid crystal display module even more preferably satisfies the equation
P=0.0016xc3x97W2.
For the purpose of improving user comfort, the main apparatus of the present invention is preferably open in the area at the top of the head. In addition, a housing portion of an optical system containing the image display means and the enlarging means, and a frontal region support cover extending from this optical system housing space at an angle following the shape of the frontal region are preferably provided in the main apparatus, and the inside surface of this frontal region support cover is preferably the frontal region support member. This is to prevent the main apparatus from sliding off.
Furthermore, when a housing portion of an optical system is provided, and a dividing wall dividing this housing portion of the optical system is provided on the face side in the main apparatus, recessed members recessed toward the optical system housing space are preferably formed in the dividing wall in the area where the nose is positioned.
Furthermore, a semi-transparent shade cover is preferably provided pointing down at the front side of the main apparatus. In this case, the shade cover is preferably of a size assuring a downward field of view. This is to enable the user to see the floor area, and thereby improve safety.
For the purpose of reducing the weight of the main apparatus and improving the degree of freedom in design, the drive circuit for the image display means is preferably provided on a flexible circuit board, and this flexible circuit board is preferably placed along the inside of the main apparatus.